The present invention relates generally to pre-loaded spring mechanisms or assemblies and, more particularly, to a method and apparatus for adjusting the pre-load of a spring in a pre-loaded spring mechanism.
Springs are used in assemblies and mechanisms as a device for storing energy as a function of displacement. Energy is supplied to, and stored in, the spring by applying a force through a suitable mechanism to compress the spring. The stored energy is released from the spring by allowing it to extend through a displacement. This energy may be used as a source for motive power (including return motion), shock absorbers, vibration control, force measurement, and the like.
Often, mechanisms or assemblies that include a spring are designed to pre-load the spring to a desired pre-load setting as may be required for a particular application. Thus, the pre-loaded spring mechanism typically includes one or more structural elements that apply an axial force to the spring to compress the spring to the desired pre-load setting. In the example of an armature used to close a valve, if the pre-load of the spring is too high or too low, the armature may unexpectedly close the valve, or may fail to close the valve when doing so is necessary. In some instances, a device may have several springs, each of which should have a similar pre-load. However, each spring will exhibit its own spring characteristic and it is therefore extremely difficult to assemble a mechanism wherein all springs will have an equal pre-load. However, equal pre-loads in the multiple springs of such a mechanism may be necessary for proper and efficient operation of the device.
Since manufacturing springs with identical spring characteristics is not practical, pre-loaded spring mechanisms in the past have accounted for variations in spring pre-load by swapping shims of different thicknesses or by incorporating adjustable set screws that vary the compression of the spring. The drawbacks of these spring pre-load adjustment methods is that the assembly must be disassembled to accomplish this task, and the pre-load adjustment process is typically time consuming and inefficient.
While the invention will be described in connection with certain embodiments, it will be understood that the invention is not limited to these embodiments. On the contrary, the invention includes all alternatives, modifications and equivalents as may be included within the spirit and scope of the present invention.
In accordance with the principles of the present invention, an apparatus and method are provided for adjusting the pre-load of a spring in a pre-loaded spring mechanism. The pre-loaded spring mechanism includes a piezoelectric device operatively coupled to a pre-loaded spring. A voltage source is operatively coupled to the piezoelectric device to apply a voltage to the device. The applied voltage causes the piezoelectric device to undergo a physical dimensional change that changes the pre-load of the spring. The pre-load of the spring is adjusted by selectively varying the voltage applied to the piezoelectric device. Different voltages can be applied to different piezoelectric devices in a spring mechanism having multiple pre-loaded springs so that each spring exhibits generally the same spring pre-load.